During angioplasty procedures it is often necessary to remove the dilatation catheter and leave the guidewire across the stenotic segment. This is required, for example, to exchange one dilatation catheter for another dilatation catheter or other therapeutic or diagnostic device. To do so requires manipulation of lengthy exchange wires, which is time-consuming and awkward to the extent that two operators are required. A current approach to dealing with this is the "monorail" system wherein a dilatation catheter has a structure such that only the distal portion of the catheter tracks a guidewire. Examples of such systems are described in Yock, U.S. Pat. Nos. 5,040,548 and 5,061,273, Bonzel, U.S. Pat. No. 4,762,129, and Kramer, U.S. Pat. No. 5,135,535, all of which are incorporated herein by reference.
In the known monorail systems the pushing force on the dilatation catheter is eccentric to the guidewire, such that there is not total responsiveness in the system as the operator attempts to manipulate the dilatation catheter along the guidewire. This can cause binding and failure to move the catheter through tortuous arterial segments and tight stenoses. In these circumstances an over-the-wire design, wherein the guidewire is within a lumen of the length of the catheter, provides superior tracking and transmission of axial force to cross tight stenoses. Thus, there is a need for an over-the-wire type catheter that can be rapidly and easily removed from the guidewire, without need to exchange the guidewire. Furthermore, it is advantageous to use as a subsequent catheter a monorail system such as is described in commonly assigned, co-pending U.S. patent application Ser. No. 07/969,887, filed Oct. 30, 1992, wherein there is co-linear design between a pushing wire and the guidewire and thus more positive tracking.